ORIGINAL: GreenAce92
Wait how big is the diesel engine and how are you going to control the engine in the first place? what happens when the diesel fuel runs out and the sub is unbalanced? I guess anything is possible if you see it in your head possible then it is.
These guys make great modules
http://www.jjc-electronics.com/
Easy to use a spare channel to switch it off, either use a servo controlling a micro switch to intrupt power to the sound module or a neater way is to use an electronic switch like the ones Subtech sell. You may even be able to rig up a water level sensing switch at will automaticall switch it off when you dive, without having to resort to a spare rc channel.